1. Technical Field
This invention relates to apparatus for determining the rolling and wear-resistance of tires and, in particular, to the roadwheel structure which is utilized with such apparatus. Such tire testing apparatus is employed to test pneumatic tires at greater speeds of rotation, the improved roadwheel permitting much greater speeds of rotation with greater accuracy of measurements, and greater margins of safety in the roadwheel structure.
2. Background Information
In the manufacture of tires and, particularly pneumatic tires used for passenger vehicles, trucks, vans, trailers, and the like, the tires are subjected to tire-rolling resistance measurement tests to be certain that the same meet prescribed test standards. Such measurements normally are obtained by placing a freely-rotatable mounted tire in contact with a driven loadwheel or wheels which are commonly called a roadwheel. Various types of measurements are obtained employing load cells which calculate the amount of resistance to rolling movement of the tire. Prior art testing apparatus is increasingly sophisticated and the tires are subjected to increasingly greater rotational speeds, the roadwheels requiring more durable and safer constructions.
The prior art roadwheels have been essentially right-cylindrical in shape, having one or more radially-extending web members which are formed parallel to the plane of rotation of the wheel. An important factor effecting prior test results is the inherent friction which is naturally present in bearing mountings of both the test tire and the roadwheel or wheels. As the roadwheels are rotated at increasingly greater speeds, the centrifugal forces generated at the higher speeds create both greater centrifugal forces on the roadwheel and its elements of construction. When the roadwheels are subjected to speeds of the order of 1000 to 1500 revolutions per minute, for example, the load wheel must provide greater margins of safety against its self-destruction when placing various load levels on the wheel by tangential contact with the tires being tested.
Some examples of prior art tire testing machines and apparatus are disclosed in U.S. Pat. Nos. 3,498,125, 3,543,576, 3,948,095, 4,171,641, 4,233,838, 4,238,954 and 4,324,128. However, none of the known prior art tire testing machines and apparatus provide any significant improvements in the roadwheel element which is especially adapted to high speeds of rotation.
U.S. Pat. No. 4,829,815 discloses tire testing apparatus in which friction is effectively eliminated by rotating the outer race of the supporting bearings at approximately the same speed as the inner race, thereby eliminating relative motion between the bearing elements and accordingly eliminating bearing losses.
U.S. Pat. No. 4,856,324 discloses a high-speed tire testing device which compensates for the elastic deformation of the structural components that support the tire during the loading of the tire against the roadwheel.
Essentially, none of the prior art devices are directed to improvements in the roadwheel for higher test speeds of rotation which will both insure safety of the apparatus during test procedures, as well as to permit more sophisticated measurements of tires when tangentially driven by the roadwheel.